1. Field of the Invention
The present invention relates to a liquid crystal display driving device, and more specifically to a device for reducing an output deviation in a liquid crystal display driving device.
2. Description of Related Art
Referring to FIG. 1, there is shown a block diagram of a prior art liquid crystal display driving device, in which analog video data supplied through a video signal input terminal 15 is converted into digital data by an A/D (analog-to-digital) converter 17, and then, inputted into a ROM table 18. This ROM table 18 carries out a so-called .gamma.-compensation (gamma compensation) by adding the inputted digital data with a previously measured or calculated output deviation compensating component. The .gamma.-compensated data is supplied to a liquid crystal display drive circuit comprising a shift register 20, a latch circuit 21 and a D/A (digital-to-analog) converter 22 which are controlled by a latch signal supplied from a latch signal input terminal 16, and also through a group of output amplifiers 23 to a group of output terminals 19 which are connected to a liquid crystal display.
The liquid crystal display driving device utilizing the .gamma.-compensation is disclosed by, for example, Japanese Patent Application Pre-examination Publication No. JP-A-1-167794 and U.S. Pat. Nos. 5,483,256 and 5,604,511, the contents of which are incorporated by reference in its entirety into this application. Also, an English abstract of JP-A-1-167794 is available from the Japanese Patent Office and the content of the English abstract of JP-A-1-167794 is also incorporated by reference in its entirety into this application.
In the above mentioned liquid crystal display driving device, since the ROM table is used, and since the .gamma.-compensation of the data is executed for each output terminal, the compensation table data is required for all the output terminals. In a multi-output driving device, therefore, a large-capacity ROM becomes necessary. In addition, since the output deviation is different from one liquid crystal display driving device to another because of variation in a manufacturing process, it is necessary to write a large amount of compensating coefficients into the ROM for each liquid crystal display driving device, and therefore, the ROM is required to have a large capacity. Furthermore, since the compensating coefficients written into the ROM have already become fixed, it is no longer possible to comply with change in temperature or a change-with-time of the liquid crystal display driving device and the liquid crystal display, such as a power supply voltage variation in the liquid crystal display driving device.